In modern society, many of the products we own or consume are manufactured. Such products are typically manufactured by industry in relatively large or very large quantities. Indeed, much of modern industry is based on the manufacture of finished products or parts to be used in products. Generally, most manufacturing is done on an assembly line or an assembly station, whether it is done by hand or done by an automated process, or a combination of both. In any event, the process is very repetitive since the main purpose is to produce a large quantity of similar or same products.
Originally, all types of manufacturing, including repetitive manufacturing, were done by hand, or at least virtually all by hand, with the aid of appropriate tools. During the industrial revolution, many manufacturing processes were mechanized to a degree, although generally to a very rudimentary degree by most modern standards. Indeed, these manufacturing processes still relied very highly on human effort to produce an end result , whether it be a part or a finished product. With modern advances in technology, repetitive manufacturing has become very much more automated. In very recent times, many manufacturing processes are completely automated, or at least portions thereof are completely automated. A high degree of automation is generally quite advantageous, generally for reasons such as improved quality, reduced costs, and increased volume of productivity.
The most recent thrust in terms of automation in industry, is to use robots to perform tasks such as placing and holding objects and articles during manufacturing. An advantage of this is that robots can place and manipulate articles of many different shapes and sizes very quickly and with a great deal of accuracy, even on a repetitive basis.
Robots can place and manipulate parts with a very high degree of accuracy. Depending on the particular circumstance on accuracy of 0.001", or even less, can be achieved virtually without fail on a repetitive basis. Generally it is also necessary to achieve the same degree of accuracy when placing or positioning a product, commonly referred to as a workpiece, for receiving a part from a robot.
Typically, workstations having some sort of level surface are used to retain and move workpieces located thereon such that the workpieces may be accessed by a robot. Such workstations often resemble tables and are usually referred to as indexing tables. In use, indexing tables are moved, usually rotationally, such that workpieces thereon are brought to the required position for receiving parts or to be worked on by a robot. Indexing tables are typically very heavy and it is very difficult to move the table quickly and at the same time to have the table stop such that the workpiece is positioned to within 0.001". Such accurate positioning of workpieces on indexing tables is desirable, if not necessary, for using indexing tables in conjunction with robots.
Further, it is also necessary that the drive mechanism that causes rotation of the indexing table also hold the indexing table rigidly in position--virtually without movement while being accessed by the robot.
An indexing table is typically used to move workpieces into position to be worked on by a person, a machine, or more commonly a robot or robotic arm. There are typically a plurality of stations on an indexing table, with each station adapted to receive a workpiece. The indexing table is rotated such that each station is stopped at one or more external reference points. Typically, at each external reference point a robotic arm or the like will add a piece to the workpiece or perform a task on the workpiece. A common arrangement for workstations on an indexing table is to have two workstations spaced around the indexing table, the workstations being spaced 180.degree. apart from each other. Correspondingly, there is one external reference point for each workstation. At one reference point the workpieces are placed on and removed from the workstations. At the other reference point, the workpieces are worked on.
One very important aspect of moving workpieces from workstation to workstation is the time taken for such movement. It is desirable that this time be minimized since it is non-productive time. In order to move the indexing table between workstations as quickly as possible, it is necessary to rotationally accelerate the indexing table as quickly as possible, but also smoothly to preclude any jerking effect. Such a jerking effect could cause workpieces to be disturbed or parts to fall therefrom.